How to shade an object blue outside of my two decals using cycle nodes
Your troubles arise from the fact that UV mapping affects not only the color of the texture but (obiouvsly) also their Alpha channel. When you add a bizzarre (because of UV mapping) alpha with another alpha you get your strange behaviour.

To solve you can edit the "front" UV map so that nothing is overlapping the decal except the faces you want to be textured.

Then take the first texture and color combine it with your blue, so that everything is blue except the grid; then color combine this output with the second texture, so that everything is like the first combination except where you want the second decal.

To better understand nodes behaviour, enable the "node wrangler" addon, and control click over a node: it will instantly create an "emission viewer" shader to read the node's outputs (if you Ctrl click twice on a texture node you'll see its alpha channel).